Neutron capture and total cross-section measurements on 94,95,96Mo at n_TOF and GELINA

This work was supported by the EUFRAT open-access project of the JRC Geel and received funding from the Euratom research and training programme 2014-2018 under grant agreement No 847594 (ARIEL).Capture and total cross section measurements for 94'95'96 MO have been performed at the neutron time -of-flight facilities, n_TOF at CERN and GELINA at JRC-Geel. The measurements were performed using isotopically enriched samples with an enrichment above 95% for each of the (94'95'96)M0 isotopes. The capture measurements were performed at n_TOF using C6D6 detectors and a new sTED detector. The transmission measurements were performed at a 10 m station of GELINA using a Li-6 glass neutron detector. Preliminary results of these measurements are presented.EUFRAT open-access project of the JRC GeelEuratom 84759

Pushing the high count rate limits of scintillation detectors for challenging neutron-capture experiments

One of the critical aspects for the accurate determination of neutron capture cross sections when combining time-of-flight and total energy detector techniques is the characterization and control of systematic uncertainties associated to the measuring devices. In this work we explore the most conspicuous effects associated to harsh count rate conditions: dead-time and pile-up effects. Both effects, when not properly treated, can lead to large systematic uncertainties and bias in the determination of neutron cross sections. In the majority of neutron capture measurements carried out at the CERN n\_TOF facility, the detectors of choice are the C$_{6}$D$_{6}$ liquid-based either in form of large-volume cells or recently commissioned sTED detector array, consisting of much smaller-volume modules. To account for the aforementioned effects, we introduce a Monte Carlo model for these detectors mimicking harsh count rate conditions similar to those happening at the CERN n\_TOF 20~m fligth path vertical measuring station. The model parameters are extracted by comparison with the experimental data taken at the same facility during 2022 experimental campaign. We propose a novel methodology to consider both, dead-time and pile-up effects simultaneously for these fast detectors and check the applicability to experimental data from $^{197}$Au($n$,$\gamma$), including the saturated 4.9~eV resonance which is an important component of normalization for neutron cross section measurements

Advances and new ideas for neutron-capture astrophysics experiments at CERN n_TOF

This article presents a few selected developments and future ideas related to the measurement of (n,γ) data of astrophysical interest at CERN n_TOF. The MC-aided analysis methodology for the use of low-efficiency radiation detectors in time-of-flight neutron-capture measurements is discussed, with particular emphasis on the systematic accuracy. Several recent instrumental advances are also presented, such as the development of total-energy detectors with γ-ray imaging capability for background suppression, and the development of an array of small-volume organic scintillators aimed at exploiting the high instantaneous neutron-flux of EAR2. Finally, astrophysics prospects related to the intermediate i neutron-capture process of nucleosynthesis are discussed in the context of the new NEAR activation area

Advances and new ideas for neutron-capture astrophysics experiments at CERN n_TOF

This article presents a few selected developments and future ideas related to the measurement of (n,γ) data of astrophysical interest at CERN n_TOF. The MC-aided analysis methodology for the use of low-efficiency radiation detectors in time-of-flight neutron-capture measurements is discussed, with particular emphasis on the systematic accuracy. Several recent instrumental advances are also presented, such as the development of total-energy detectors with γ-ray imaging capability for background suppression, and the development of an array of small-volume organic scintillators aimed at exploiting the high instantaneous neutron-flux of EAR2. Finally, astrophysics prospects related to the intermediate i neutron-capture process of nucleosynthesis are discussed in the context of the new NEAR activation area

Scientific motivations for a reassessment of the neutron capture cross sections of erbium isotopes in the high-sensitivity thermal energy range for LWR systems

Research conducted in the last twenty years in the field of burnable absorbers showed that erbium isotopes can be considered as an excellent alternative absorber to gadolinium isotopes for their neutronic and nuclear safety improving features. The development of the Erbium Super High Burnup (Er-SHB) concept demonstrated that erbium could be directly mixed in all fuel pins of a fuel assembly (FA) at the Beginning of Life (BOL). This innovative design allows an improvement of nuclear safety, a better control of the operational and accidental transient phase and an extension of the fuel life with respect to the most used burnable absorber (i.e., gadolinium). Furthermore, the extensive use of an Er-SHB fuel design would allow the production of higher enriched nuclear fuel (i.e., >5 wt%) within the existing manufacturing facilities without any modification of the facility itself and with a general improvement of the nuclear safety of the front-end phase of the nuclear fuel cycle. Nevertheless, reported erbium cross-sections are dated and poorly investigated in the high sensitivity thermal energy region for nuclear technology. In addition, some of them (i.e., Er-166) are reported with an uncertainty that is too high for their use in the future design of the erbia-doped LWR assembly by the industry. On the other hand, evaluated uncertainties by the ENDF/B-VIII.0 library in the thermal/epithermal region for the most sensitive isotopes (i.e., Er-167) seem to be too low with respect to both the experimental data and the analysis of the results provided by some erbia-doped critical systems of the International Critical Safety Benchmark Evaluation Project (ICSBEP). Based on the reanalysis of the ICSBEP outcomes, and a sensitivity-uncertainty analysis (S&U) on an Er-SHB LWR assembly, this article shows that recent evaluations appear inadequate to provide accurate criticality calculations for a system all equipped with erbium fuel pins for neutronic design purpose. Moreover, the S&U results have shown the importance of erbium isotopes to correctly evaluate the uncertainty associated with a Light Water Reactor (LWR) critical system. They confirmed the need for a re-evaluation of their neutron capture cross section by means of a new experimental campaign. A proposal aiming at performing a new capture measurement of erbium isotope cross sections has already been submitted to GELINA facility at Geel (Belgium), which is particularly suitable for neutron capture and transmission measurements in the thermal and epithermal energy regions. On August 2021, U.S. Nuclear Energy Agency (NEA) added the revaluation of Er-167(n, γ) in its High Priority Request List (HPRL) based on the outcomes reported in this work. On January 2022, GELINA Scientific Committee accepted the proposal within the 2021 calls for open access to JRC Research Infrastructures in the research filed of European Research for nuclear reaction, radioactivity, radiation and technology studies in science and application (EUFRAT)

Presolar Grain Isotopic Ratios as Constraints to Nuclear and Stellar Parameters of Asymptotic Giant Branch Star Nucleosynthesis

Recent models for evolved low-mass stars (with M ≲ 3 M o˙), undergoing the asymptotic giant branch (AGB) phase assume that magnetic flux-tube buoyancy drives the formation of 13C reservoirs in He-rich layers. We illustrate their crucial properties, showing how the low abundance of 13C generated below the convective envelope hampers the formation of primary 14N and the ensuing synthesis of intermediate-mass nuclei, like 19F and 22Ne. In the mentioned models, their production is therefore of a purely secondary nature. Shortage of primary 22Ne has also important effects in reducing the neutron density. Another property concerns AGB winds, which are likely to preserve C-rich subcomponents, isolated by magnetic tension, even when the envelope composition is O-rich. Conditions for the formation of C-rich compounds are therefore found in stages earlier than previously envisaged. These issues, together with the uncertainties related to several nuclear physics quantities, are discussed in the light of the isotopic admixtures of s-process elements in presolar SiC grains of stellar origin, which provide important and precise constraints to the otherwise uncertain parameters. By comparing nucleosynthesis results with measured SiC data, it is argued that such a detailed series of constraints indicates the need for new measurements of weak-interaction rates in ionized plasmas, as well as of neutron-capture cross sections, especially near the N = 50 and N = 82 neutron magic numbers. Nonetheless, the peculiarity of our models allows us to achieve fits to the presolar grain data of a quality so far never obtained in previously published attempts

A two-layer Timepix3 stack for improved charged particle tracking and radiation field decomposition

We characterize a novel instrument designed for radiation field decomposition and particletrajectory reconstruction for application in harsh radiation environments. The device consists oftwo Timepix3 assemblies with 500 µm thick silicon sensors in a face-to-face geometry. Thesedetectors are interleaved with a set of neutron converters: $^{6}$LiF for thermal neutrons,polyethylene (PE) for fast neutrons above 1 MeV, and PE with an additional aluminum recoil protonfilter for neutrons above ∼4 MeV. Application of the coincidence and anticoincidencetechnique together with pattern recognition allows improved separation of charged and neutralparticles, their discrimination against γ-rays and assessment of the overall directionalityof the fast neutron field. The instrument's charged particle tracking and separation capabilitieswere studied at the Danish Center for Particle Therapy (DCPT), the Proton Synchrotron, and SuperProton Synchrotron with protons (50–240 MeV), pions (1–10 GeV/c and 180 GeV/c). After developingtemporal and spatial coincidence assignment methodology, we determine the relative amount ofcoincident detections as a function of the impact angle, present the device's impact angleresolving power (both in coincidence and anticoicidence channels). The detector response toneutrons was studied at the Czech Metrology Institute (CMI), at n_ToF and the Los Alamos NeutronScience Center (LANSCE), covering the entire spectrum from thermal up to 600 MeV. The measuredtracks were assigned to their corresponding neutron energy by application of the time of flighttechnique. We present the achieved neutron detection efficiency as a function of neutron kineticenergy and demonstrate how the ratio of events found below the different converters can be used toassess the hardness of the neutron spectrum. As an application, we determine the neutron contentwithin a PMMA phantom just behind the Bragg-peak during clinical irradiation condition withprotons of 160 MeV

Neutron capture and total cross-section measurements on Mo-94'95'96 at n_TOF and GELINA

Capture and total cross section measurements for 94'95'96 MO have been performed at the neutron time -of-flight facilities, n_TOF at CERN and GELINA at JRC-Geel. The measurements were performed using isotopically enriched samples with an enrichment above 95% for each of the (94'95'96)M0 isotopes. The capture measurements were performed at n_TOF using C6D6 detectors and a new sTED detector. The transmission measurements were performed at a 10 m station of GELINA using a Li-6 glass neutron detector. Preliminary results of these measurements are presented.Comunidad Europea de Energía Atómica (Euratom) 84759